Many innovations for optical communication systems have involved the manner in which light waves are switched and manipulated. In many optical transmission applications, it is necessary to perform one or more of the following actions on light: switching, wavelength conversion, attenuation, waveform amplification/reshaping/retiming (1R/2R/3R), routing to different locations or manipulating the phase or polarization of light. Such actions are critical for realization of the optical networks that are the foundation of global communications systems.
Optical communication systems increasingly employ wavelength division multiplexing (WDM) techniques to transmit multiple information signals on the same fiber, and differentiate each user sub-channel by modulating a unique wavelength of light. WDM techniques are being used to meet the increasing demands for improved speed and bandwidth in optical transmission applications. In optical communication networks, such as those employing WDM techniques, individual optical signals are often selectively routed to different destinations. Thus, a high capacity matrix or cross-connect switch is often employed to selectively route signals through interconnected nodes in a communication network.
At the heart of these cross-connect switches is the single switching unit. Electronic optical switches first convert an optical signal into an electrical signal to perform the switching and then convert the electrical signal back into optical signals. These conversions are very expensive and the switches are complex to manage but allow considerable flexibility. As networks grow and become dense, however, electronic switches become increasingly expensive and harder to fabricate.
Therefore, optical switches that operate directly on the light wave are favorable. Optical switches are often realized in optical waveguides that can be manufactured with low cost and enable easy multiplexing and de-multiplexing of the WDM signal using waveguide grating routers (WGR). For a detailed discussion of waveguide grating routers, such as those composed of optical star couplers and wavelength dependent beam forming, see U.S. Pat. No. 4,904,042 to Dragone.
Currently available optical switches, however, allocate an entire wavelength to each packet in order to permit wavelength selective routing. Wavelengths that can be exploited for optical communications are finite in number and expensive to provision. Thus, an entire wavelength is a rather large granularity for resource allocation in an optical communication system. A need therefore exists for a more efficient mechanism for switching optical signals at the wavelength level, especially at the core of an optical network. A further need exists for a scalable approach for implementing systems comprised of large number of optical flows, and a heterogeneous mix of ever increasing information rates upon each such flow.